DESCRIPTION: The development of hematopoietic defined protein-free reagents that support megakaryocyte formation will be of inestimatable importance. The rationale for developing such reagents is that it will allow the measurement of drug toxicity in its unbound state in which all of the drug is active. The advantages to such reagents are they will be uniform standard reagents for such assays, save investigator time and effort in developing such reagents and facilitate drug evaluation free of bond drug. This proposal combines the strengths of two laboratories, one skilled in development of protein-free and serum-free reagents and the other in megakaryocyte assay. Such a combination should bode well for the success of this proposal. The Phase I effort will focus on the development of defined reagents for a murine megakaryocyte assays and, as time permits, and in the Phase II effort the development of defined reagants for human megakaryocyte assays.